Radiopharmaceuticals such as fludeoxyglucose (FDG) used in nuclear medical imaging such as positron emission tomography (PET) are produced in cyclotrons, from bombardment of a target material with charged particles. A cyclotron is a particle accelerator that comprises two metal D-shaped electrodes placed in a vacuum chamber between two poles of a large magnet. Typically, negatively charged particles (anions) are injected into the center of the chamber via a high voltage ion source. A high frequency alternating voltage applied between the two electrodes dramatically increases the kinetic energy of the particles and the strong magnetic field forces them to travel in a spiral pathway as a beam from the center towards the perimeter of the vacuum chamber where the beam interacts with a stripping foil. The interaction results in the removal of electrons from the accelerated particles, transforming them into positively charged particles. The positive charge of the particles alters the pathway of the accelerated beam, which exits the vacuum chamber and collides with the content of the target yielding positron emitting radionuclides. For the production of fluorine-18, the accelerated particles are usually hydrogen (protium) and the target material is oxygen-18, typically in the form of enriched water. This process is called bombardment and the longer it lasts the more fluorine-18 is produced which in turn will be used to synthesize larger quantities of FDG.
Due to their unstable nature, fluorine-18 radionuclides undergo radioactive decay immediately after they are created in the bombardment process stage causing the quantity of radioactivity due to fluorine-18 to decrease. The length of time for the radioactivity to reach half of the initial amount is called half-life and for fluorine-18 it is 109.771 minutes. This relatively long half-life makes fluorine-18 an ideal radionuclide for medical imaging for two main reasons: (a) it can be transported to a substantial distance from the production facility, a radiopharmacy, and (b) after about 10 hours it is substantially eliminated from the patient's body.
A fundamental practice in every radiopharmacy is the creation of a daily schedule for the production of FDG in batches and the dispensing of the FDG into corresponding patient doses. An individual batch may provide sufficient radioactivity for up to forty or more individual doses for injecting into a patient. The number of doses that can be served by a batch depends on the distance between the radiopharmacy and the customers, nuclear imaging centers or hospitals, as well as the actual injection time of each dose. The farther a customer is from the radiopharmacy, the more radioactivity needs to be produced and therefore the bombardment process within the cyclotron needs to last longer. It is therefore important to accurately determine the amount of radioactivity that needs to be produced in order to meet the demand for the FDG for a large number of geographically dispersed customers.
Currently, in most radiopharmacies, the daily schedule for production of FDG is manually generated by radiopharmacists. Although radiopharmacists have great domain knowledge and experience, the manual generation of the schedule is a time-consuming process and may result in sub-optimal production schedules that either produce too much fluorine-18 than necessary or insufficient amount of fluorine-18. This results in excess labor costs and wasting the excessive amount of radioactivity which wastes resources and increases the production cost or not being able to completely meet the demand placed by medical imaging centers and/or hospitals. Thus, there is a need for an improved method of generating the production schedule for radiopharmaceuticals such as FDG so that FDG is produced in sufficient quantity to meet the demand without producing too much excess so that waste is minimized.